The present invention generally relates to vehicle stability control, and more particularly relates to a control circuit for controlling the driving stability of a vehicle in which the input quantities defining the course of the vehicle are input to a vehicle model circuit.
The control circuits control the steering behavior of the vehicle, if the vehicle""s path does not correspond to the path intended by the driver.
Especially in case of external influences, e.g. different adhesion on wet, icy or dry road sections, side wind and reactions to load alternations, an additional torque is necessary so that the way actually covered by the vehicle corresponds to the way intended by the driver.
Input quantities resulting from the path intended by the driver, e.g. steering wheel angles or speed, are transmitted to a vehicle model circuit which on the basis of said input quantities and parameters typical for the driving behavior of the vehicle, but also on the basis of the characteristics of the environment (coefficient of friction of the road surface and similar) defines a nominal yaw rate being compared with the actually measured yaw rate. The difference between the yaw rates is converted into a yaw torque by means of a so-called yaw torque controller, the yaw torque representing the input quantity of the control circuit.
The control circuit, on the other hand, defines the brake pressure to be applied on the single wheel brakes, if necessary subject to the driver""s request to apply a certain brake pressure on the wheel brakes. In addition to the desired braking effect, the brake pressure should create an additional torque on the vehicle supporting the driving behavior of the vehicle in the direction in which the driver intends to steer the vehicle. From this results that the quality of controlling the yaw rate of the vehicle is substantially defined by the quality of the vehicle model circuit which predefines the desired yaw rate on the basis of the input data of the driver.
Different vehicle models can be used in the control circuit which simulate the driving behavior of the vehicle by way of calculation, the different vehicle models being based on simplified assumptions concerning the driving behavior of a vehicle.
A known vehicle model is the so-called linear dynamic single-track model. In this model the driving characteristics of a vehicle are reduced, by way of calculation, to one vehicle model in which the front and rear wheels each are combined in pairs to one wheel being positioned on the longitudinal axis of the vehicle.
The following system equations are valid for a single-track model in a condition representation:                               β          .                =                                            c              11                        ⁢                          β              v                                -                      ψ            .                    +                                    c              12                        ⁢                                          ψ                .                                            v                2                                              +                                    c              13                        ⁢                          δ              v                                                          (        1        )                                          ψ          ..                =                                            c              21                        ⁢            β                    +                                    c              22                        ⁢                                          ψ                .                            v                                +                                    c              23                        ⁢            δ                                              (        2        )            
xcex2 defining a slip angle, {dot over ("psgr")} the yaw rate and xcex4 the steering angle.
The model coefficients Cii are included in the system equations and formed as follows:                               c          11                =                                            -                                                                    c                    h                                    +                                      c                    v                                                  m                                      ⁢                          xe2x80x83                        ⁢                          c              12                                =                                                                                                                c                      h                                        ⁢                                          l                      h                                                        -                                                            c                      v                                        ⁢                                          l                      v                                                                      m                            ⁢                              xe2x80x83                            ⁢                              c                13                                      =                                          c                v                            m                                                          (        3        )                                          c          21                =                                                                                                  c                    h                                    ⁢                                      l                    h                                                  -                                                      c                    v                                    ⁢                                      l                    v                                                              Θ                        ⁢                          xe2x80x83                        ⁢                          c              22                                =                                                                                                                c                      h                                        ⁢                                          l                                              h                        2                                                                              +                                                            c                      v                                        ⁢                                          l                                              v                        2                                                                                            Θ                            ⁢                              xe2x80x83                            ⁢                              c                23                                      =                                                            c                  v                                ⁢                                  l                  v                                            Θ                                                          (        4        )            
Ch and cv represent the resulting stiffness determined by the control circuit for controlling the driving stability of the vehicle in consideration of the wheel suspension and steering elasticity on the rear resp. front axle. The values lh and lv represent the distances of rear and front axle from the vehicle""s gravity centre. "THgr" is the yaw moment of inertia of the vehicle, i.e. the moment of inertia of the vehicle around its vertical axis.
The standard parameters for the memorized single-track model which form the basis of the model coefficient cii, are obtained by measurements outside the vehicle on the basis of an off-line parameter identification. The measured controller and sensor quantities of the driving stability control are used for identification. Four speed sensors, one for each wheel, a yaw acceleration meter, a transverse acceleration meter and at least one pressure sensor for the brake pressure generated by the brake pedal are provided on the vehicle in order to detect the vehicle dynamics. The parameters are determined by means of one or more model vehicles, and the xe2x80x9cstandard parameter setxe2x80x9d is memorized in the vehicle model circuit.
During travel, vehicles with standard parameter sets memorized in the vehicle model present erroneous control activation by means of the driving stability control, if the condition quantities on which the model coefficients are based during off-line parameter identification, differ from the actual condition quantities being defined by the individual configuration or equipment of the vehicle. The deviations may range from a mere comfort problem to an impairment of the driving behavior of the vehicle. There is an erroneous control activation by the driving stability control if the individual configuration of the vehicle leads to deviations of the standard parameters memorized in the dynamic single-track model or if the parameters on which the vehicle is based due to its individual configuration are lying outside the control threshold of the standard parameters.
One known solution to the problem is to expand control thresholds in critical areas of the vehicle stability. This leads to functionality and performance losses due to an unnecessary threshold expansion in vehicles with an individual configuration or equipment which is detected by the standard parameters defined in the single-track model and does not prevent reliably the erroneous control activation if there are extreme deviations with regard to the configuration or equipment of a single vehicle.
It is the object of the present invention to provide for a generic control circuit preventing the erroneous control activation. This object is achieved according to the present invention by that at least one of the parameters is varied subject to at least one separately defined measuring quantity.
The invention includes a generic control circuit that is used in such a way that the vehicle model is adapted during operation by the identification of the standard parameters specific to the every single vehicle by means of input quantities which are made available by the vehicle""s sensor system. Basis of the invention is the finding, that the individual vehicle due to different configuration or equipment variants, as e.g. tire type (winter tires, summer tires, all-weather-tires), tire size (15xe2x80x3/16xe2x80x3/17xe2x80x3), condition, especially the lateral tire stiffness, changes of the chassis, production tolerances or loading, differs or deviates considerably from a model vehicle or model vehicles which are used for determining the standard parameter set memorized in the single-track model.
One advantageous embodiment of the control circuit is characterized by that a vehicle identification means is foreseen, the output signals of which are transmitted to the vehicle reference model and that the output signals in consideration of individual condition quantities of the vehicle adapt the standard parameters memorized in the vehicle reference model or substitute them by newly built standard parameters.
A further improvement of the control circuit is achieved wherein the vehicle identification means is provided with an identification plausibility means for switching an identification module into active or passive mode subject to the individual input quantities.
Furthermore it is useful to configure the control circuit in such a way that the yaw speed and/or the steering angle and/or the steering angle speed and/or the transverse acceleration and/or the longitudinal acceleration and/or the slip angle speed and/or the wheel speed are the quantities being input.
One advantageous embodiment of the control circuit is characterized by that the deviations are defined by individual input quantities and deviations of the standard parameters or actual standard parameters are generated by means of an identification algorithm.
A further improvement of the control circuit is achieved wherein a computing unit the deviations of the single input quantities are converted into parameter deviations of the standard parameters or actual standard parameters.
It is also useful to configure the control circuit in such a way that the identification plausibility means for informs the identification module as to whether the individual input quantities are lying in a predetermined tolerance range.
One advantageous embodiment of the control circuit is characterized by that the parameter deviations of the standard parameters or the actual parameters are defined within predetermined limit value ranges.
A further improvement of the control circuit is achieved by that the parameter deviations of the standard parameters or the actual standard parameters are learned by algorithms for the parameter identification.
Furthermore it is useful to configure the control circuit in such a way that parameter deviations of the standard parameters or actual standard parameters a learned according to a Least Square Procedure (LS;) and/or a Generalized Least Square Procedure (GLS) and/or an Instrumental Variable Procedure (IV) and/or a Maximum Likelihood Procedure (ML) and/or an Output Error Procedure.
One advantageous embodiment of the control circuit is characterized by that the vehicle reference model is the dynamic single-track model.
A further improvement of the control circuit is achieved by that at least one of the parameters corresponds to the lateral tire sniffiness of one or more wheels or depends on the lateral tire stiffness of one or more wheels.
Thus it is assured that a possibly big reference quantity is made available for controlling the vehicle in every driving situation with individually adapted parameters.
Empirical studies resulted in the following deviations of the standard parameters when several driving conditions were identified:
Since a vehicle identifying means is foreseen the output signals of which are transmitted to the vehicle reference model, and since the output signals adapt the standard parameters memorized in the vehicle reference model to the individual vehicle in consideration of the individual condition quantities of the vehicle or substitute them by newly built standard parameters, every vehicle is displayed online in the vehicle model according to its configuration or equipment. Erroneous control activations are reliably avoided since even in case of extreme tires the relative model coefficients cii are adapted. By learning the vehicle-specific standard parameters during given driving conditions and their actualization depending on time or on the driving condition or the driving behavior of the vehicle, not only the fixed configuration and/or equipment variants assigned to the vehicle, especially of the torque, are considered, but also the changes resulting from the vehicle motion, e.g. the tire temperature, are detected and considered. During travel, the vehicle parameters are adapted to the real individual vehicle behavior by means of the input quantities measured by the vehicle sensors.
In an advantageous embodiment the vehicle identification means includes an identification plausibility means which subject to the individual input quantities switches an identification module into active or passive mode. By the foreseen identification plausibility means for the parameters are identified only during a stable travel since only in this condition the identification module is switched to the active mode thus permitting to learn the standard parameters. It is reliably avoided that the identification module is activated during an unstable travel.
According to one embodiment, the stable travel is recognized by means of measured input quantities determined individually on each vehicle subject to the condition quantities. The input quantities are equal to the yaw speed and/or the steering angle and/or the transverse acceleration and/or the longitudinal acceleration and/or the slip angle acceleration and/or the wheel speeds. In addition to this, condition quantities of other control circuits or control systems, as e.g. anti-blocking systems (ABS) or traction slip control systems (TCS), are transmitted as input quantities to the identification plausibility means. The input quantities representing the actual condition of said control circuits or control systems also serve for recognizing the stable travel, which, evaluating the above mentioned input quantities, in the identification plausibility means for is stable, if no further control circuit is active. In a stable travel e.g. the input quantity of an individual vehicle meets the following conditions:
transverse acceleration (aquer) less than 0.3 g
longitudinal acceleration (along) less than 0.1 g
yaw speed ("psgr") less than 10xc2x0/s
steering speed (xcex2) less than 90xc2x0/s
and no other control circuits are active. On the above mentioned conditions, the identification module is switched to the active mode.
According to one preferred embodiment of the present invention, in the identification module or a comparison means which is part of the identification module or the distribution logic, the deviations of the individual input quantities are determined and parameter deviations of the standard parameters or actual standard parameters are generated by means of an identification algorithm. In a preferred embodiment the identification module therefore includes a computing unit converting the individual input quantities and/or their deviations into the parameter deviations of the standard parameters or the actual standard parameters. In this case the parameter deviations of the standard parameters or actual standard parameters are learned according to the Least Square Procedure (LS) and/or Generalized Least Square Procedure (GLS) and/or Instrumentable Variable Procedure (IV) and/or Maximum-Likelihood Procedure (ML) and/or Output Error Procedure (OE). A Least Square Procedure determines the standard parameters from the deviations of the individual input parameters by minimizing the error between the vehicle reference model and the vehicle. Minimizing the sum of squares of the model error is used here as quality criterion. A direct solution can be obtained by setting the first partial derivation to zero.
Parameters are made available to the identification module by the identification plausibility means for which help determine whether the individual input quantities or their deviations between the measured actual input quantities and the nominal input quantities calculated in the controller are lying within a predetermined tolerance range. If the individual input quantities lying in the predetermined tolerance range are derived, the parameters which can be correlated to individual quantities within predetermined limit value ranges are defined.
Further advantages, particularities and appropriate improvements of the present invention result from the dependent claims and the following representation of preferred embodiments of the invention on the basis of the drawings.